They include two women, nurse Shirley Chaplin and British Airways air hostess Nadia Eweida who claim they were asked to remove necklaces with crosses on them at work, relationship counsellor Gary McFarlane who told Relate he felt uncomfortable offering advice to gay couples, and registrar Lillian Ladele who would not conduct same-sex civil partnerships.

The European Court of Human Rights will investigate whether there has been a breach of Article Nine of the European Convention of Human Rights, their right to freedom of religion.

In a submission to the court, Lord Carey said: "The secular human rights agenda has gone too far and the Convention is losing legitimacy in many Contracting states.

"Many noble words such as ‘human rights’ are seen as little more than a political agenda.

"The human rights agenda is now seen as an anti-moral agenda; the Court must restore its prestige by recognition of traditional religious values.

"Christians have values of morality, honesty and generosity that the State should promote, not discourage.

In his submission, Lord Carey argued Christians were being increasingly “vilified” and “driven underground” by the tendency of UK courts to apply "equality law to discriminate against Christians.”

As the court adjourned on Wednesday, Lord Carey accused the government of double-standards, saying: "David Cameron has turned the value of ‘tolerance’ on its head. Only two months ago he championed the right of Christians to wear crosses.

“Yet at the same time he was making that statement, his lawyers were drafting a legal submission to Strasbourg which opposes the rights of all these Christians.

"We have to question, then, whether Cameron’s initial words of support mean anything at all.

“Sadly, the Government has passed up its opportunity to support the right of Christians to express their faith and have a reasonable accommodation in the law for freedom of conscience.

“It is now down to the European Court. In these cases, Christians are not seeking special rights but merely trying to overturn unfair verdicts which create a hierarchy of rights in which Christians are at the bottom of the pile.”

Andrea Minichiello Williams, barrister and founder of the Christian Legal Centre also criticised the government's approach.

“The prime minister has been asked, repeatedly, to intervene in these cases and back the four Christians who have served the public through their varied professions. He has failed dismally.

“Many believe it is unfair that hard-working public servants and employees are being discriminated against simply because of their faith. It is very clear at the moment that there is either a major problem in the way that the Equality Act was drafted. It is time for this to be redressed.

“The working of the British courts has led to deep injustice. If we are successful in Strasbourg I hope that the Equality Act and other diversity legislation will be overhauled, so that Christians are free to work and act in accordance with their beliefs and conscience.”

Andrew Marsh, campaigns director for Christian Concern, which is providing legal support for Chaplin and McFarlane, told The Huffington Post UK that the four cases were a small example of the volume they dealt with. He said he felt they had been treated with "aggression and hostility" by their employers.

"I think the media has drawn attention to the fact that much of this is directed specifically against Christians, for whatever reason, and other faiths are more accommodated if they have specific requests at work.

"What lies at the heart of this is that no-one has been harmed by the choices these four wanted to make, no-one had had a service denied to them. This is an issue which really resonates with people on the ground, and is much wider than just a Christian issue.

"Detractors have wanted to paint Gary and Shirley as 'rights-obsessed' and belligerent, but they are extremely gentle and accommodating people."

The court is not expect to reach a verdict for a number of months.

Andrew Copson, chief executive of the British Humanist Association, expressed his hope that the European court will uphold the judgements of the British courts, which have rejected claims of religious discrimination.

"Our domestic courts have been robust in dismissing these cases and the victim narrative that lies behind them has no basis in reality. What they describe as discrimination and marginalisation of Christians is in fact the proper upholding of human rights and equalities law and principles," he said.

"All reasonable people will agree that there is scope in a secular democracy for reasonable accommodation of religious beliefs when that accommodation does not affect the rights and freedoms of others.

"But if believers try to invoke their beliefs as a defence for treating other people badly – denying them a service because they are gay or claiming a right to preach at them in a professional context – the law is right to prevent them."